Identification of Neoscytalidium dimidiatum causing canker disease of pitaya in Hainan, China

Canker disease, caused by Neoscytalidium dimidiatum, is the most severe disease affecting the pitaya (Hylocereus spp.) industry. In this study, we isolated identified and characterized this fungal pathogen, based on its morphology, molecular characteristics, and pathogenicity. One fungal strain, named N. dimidiatum 8 (ND8), was isolated from wild-type red-fleshed pitaya (H. polyrhizus) growing in Hainan Province, China. The fungal hyphae were white, then turned gray and finally changed black on potato dextrose agar plates. Under the microscope, the hyphae appeared branched, the individual conidia, arthrospore, and chlamydospore were rod-shaped. Bunchy arthrospore and chlamydospore were chain-like. The cell wall of chlamydospore was thicker than conidia and arthrospore. Diseased stems of pitaya plants initially developed small yellow spots, which gradually spread, eventually leading to the rotting of entire stems. The internal transcribed spacer (ITS) sequences of ND8 strain were 559 bp in length and showed 99% similarity to an N. dimidiatum sequence in GenBank (JX524168.1). The phylogenetic analysis also revealed that the novel isolates ND8 grouped with members of the genus Neoscytalidium. Pathogenicity test showed that pitaya plants infected with ND8 strain exhibited the same symptoms as diseased plants in plantations.